1. Field of the Invention
The present invention relates to an apparatus for picking up objects, particularly, workpieces having curved shapes, using a robot.
2. Description of the Related Art
Recently, a plurality of workpieces arranged in a disorderly manner, or a plurality of workpieces randomly positioned in a basket or pallet, are picked up by an industrial robot. Picking up so-called polyhedral workpieces from a basket, each of the workpieces having a large number of plain portions whose contour and shape feature can be stably detected, has previously been disclosed (see: “Practical Bin Picking by the Intelligent Robot”, Proc. of 36th ISR, TH311, 2005).
On the other hand, a workpiece with curved shapes has few detectable features, such as texture. Also, a workpiece with curved shapes has a problem in that its observed contour fluctuates depending upon illumination and other camera conditions. Therefore, it is difficult to detect workpieces with curved shapes, so that the use of robots to pick them up is not practical.
For example, Japanese Unexamined Patent Publication (Kokai) No. 2005-1022 discloses that a three-dimensional model for a workpiece with curved shapes is constructed to match the contour lines and textures of the workpiece.
Also, Japanese Patent No. 3252941 suggests a technique for recognizing a workpiece with curved shapes by an approach using eigenvectors.
Further, Japanese Unexamined Patent Publication (Kokai) No. 10-315167 discloses that workpiece are scanned and irradiated with a laser slit light in a mesh state so that the three-dimensional curved shape of the workpiece is recognized based on the reflected light. In this case, a three-dimensional model matching the object shape can be obtained without using contours and textures.
However, in the technique described in Japanese Unexamined Patent Publication (Kokai) No. 2005-1022, when a workpiece does not have a detectable contour or texture, such a workpiece cannot be detected.
Also, the technique described in Japanese Patent No. 3252941 assumes that a background can be completely separated from an object to be detected. As a result, the technique described in Japanese Patent No. 3252941 cannot respond to a state where a plurality of workpieces are superposed thereonto. Further, even in the technique described in Japanese Patent No. 3252941, in the same way as in Japanese Unexamined Patent Publication (Kokai) No. 2005-1022, since a texture or contour is required, it is difficult to precisely recognize a workpiece such as a simple cylinder.
Further, in the technique described in Japanese Unexamined Patent Publication No. 10-315167, complex and expensive equipment is required to obtain three-dimensional shape data. Additionally, since extensive calculating processing is usually required to calculate three-dimensional data, it is difficult to put the system described in Japanese Unexamined Patent Publication (Kokai) No. 10-315167 into practical use.
In view of the above-described circumstances, an object of the present invention is to provide an apparatus for picking up objects capable of detecting and picking up a workpiece with a curved shape whose texture is slight and whose contour is unclear, in a reasonably short period of time.